Frequency modulation system



A. H. TAYLOR FREQUENCY MODULATION SYSTEM Filed April 18. 1929 Oulyur Output ATTORNEY Nov. 17, 1931.

Patented Nov. 1.7, 1931 UNITED STATES- PATENT OFFICE ALBERT n. Tanon., or WASHINGTON, DISTRICT or centrum, assienon. To

`B.A.'D1O, ING., OI' NEW YORK, N. Y., .A CORPORATION 0F DELAWARE FREQUENCY MODULATION SYSTEI Application led April 18,

My invention relates to the frequency modulation of piezo electrically controlled c ircuits in general and more particularly to slgnaling systems.

One of the objects of my invention is to provide means for modulating the frequency of a piezo electric control circuit.

Another object of my invention is to prorent; Fig. 2 shows a frequency modulating arrangement where the modulating source may be any form of mechanical energy; Fig. 3 shows a modification of the arrangement shown in Fig. 1; and Fig. 4 shows still another modication wherein the frequency of the piezo electrically controlled circuit is modulated in accordance with sound or audio frequencies.

Current modulation has been employed heretofore in the art whereby the energy of the carrier frequency from a high frequenc generator is modulated in accordance wit frequency of a lower order. This may be called energy modulation as contrasted with .frequency modulation employed in accordance with my invention. Energy modulation has a number of disadvantages as pointed out in my c'oending application, Serial No. 339,139, filed ebruary 11, 1929. Frequency modulation 1s preferable in many instances especially where the band of frequencies occupied by energy modulation would be ex- Fig. 1 of the accompanying drawings is a schematic circuit diagram representing a typical iezo electric oscillator circuit. Thermiomc tube 1 is shown as of the three electrode type, however. it is obviousthat tubes havin electrodes other than a cathode 2, contro 'and actuated thereby.

1929. Serial N0. 356,179.

electrode 3 and anode 4 may be employed. Cathode 2 is energized by source 5. Anode 4 is ener 'zed by source 6, through high frequency c oke coil 7. Control electrode 3 is suplplied with a biasing potential from source 8 t rough hlghfrequency choke coil 9. Piezo electric element 10 may be a suitable mechanically vibratile element such as quartz and the like associated with control electrode 3 and cathode '2 of thermionic tube 1 by means of electrodes 11 and 12. Anode 4 of thermionic tube 1 is coupled to inductance 14 by condenser 13, the latter serving to prevent shortcircuiting of source 6. The frequency characteristics of the output circuit of inductance 14 are controlled by adjustable condenser 15.

Orinarily, the part of the circuit described thus far constitutes an oscillatory circuit, the generated energy having a frequency as determined by the frequency characteristics of element 10. The generated energy may be delivered to any circuit desired by output connection 16. c

It has been found that variations in the frequency characteristics of the anode circuit 14-15, in such circuits as are shown herein, produce variations in the frequency of the energy transferred to the output circuit. If, for instance, piezo electric element 10 has a fundamental or natural fre uency of 4000 kilocycles, variations in the requency from this value to the extent of several hundred cycles can be obtained by effecting small variations in the freriency characteristics of the circuit 14-15. any arrangements may be employed for causing this variation in the frequency characteristics of circuit 14-15, some of which are illustrated in the accompanying drawings. f

In Fig. 1 this change in the frequency of the energy transferred to-the out ut 16 is effected in a simple manner. A re ay is employed which is shown as comprising a core member 20, and windings 21. An armature 19 is magnetically related to core member 20 Armature A19 carries a contact member adapted to contact with stationary contact member 18. Armature 19 is electrically connected to one end of inductance 14. Contact member 18 is posi? while tioned adjacent to the contact member carried by armature 19 and is electrically connected to one terminal of condenser 17.

The other terminal of condenser 17 is con- 6 nected to a portion of inductance 14 whereby an opposite potential is impressed upon the opposite plates constituting condenser 17. Windings 21 are connected with any suitable source of alternating current supply which m may or may not be periodically interrupted. When such supply energizes winding 21, armature 18 is actuated, thereby causing periodic interruption of the circuit between condenser 17 and inductance 14. The frequency characteristics of circuit 14-15 are changed at the rate of interruption to an amount determined by the capaclty of condenser 17 and the lalimount of inductance 14 connected therewit Fig. 2 of the accompanying drawings is a schematic circuit digaram showing a chopper wheel 19a which periodically makes electrical contact with stationary contact member 18. VChopper wheel 19a is revolved by motor 24, the latter energized by any convenient source of electrical energy. Reference characters correspond in all the drawings. `The rate of interruption is determined by the chosen design of chopper wheel 19a and the speed of motor 24. 1

Fig. 3 is a schematic circuit diagram showing a modification of the system I em loy for the frequency modulation ofl signa ing energy. n my arrangement the movable plate carried by armature 19 of relay 20 is periodically moved nearer to and farther away from the stationary plate of condenser 17. This effects a change in frequency the frequency at each instant being proportional to the p0- sition of the movable plate with respect to the position of the stationary plate. The a-.rrangements shown in Figs. 1 and 2 proyide a rapid change in frequency between two values while the arrangement shown in Fig. 3 provides a variable frequency the rate of variation being proportional to the movement of armature 19. A motor might be provided to vary the capacitive relation of the plates constitutingr condenser 17. w Fig. 4 shows still another modification 1n that the frequency modulation is effected by sound energy. The condenser 17 for effecting the frequency modulation comprises plates 17a and 175. 4'Plate 17a may be fixed plate 17 b may be movably mounted and adapted to be actuated by sound waves. Sound waves directed against plate 17b, which may be termed a diaphragm, cause the distance between plates 17a and 1712 to vary 62, thereby varying the capacity and hence varying the frequency of the generated energy.

Signals from the oscillator may be observed on a receiver in connection with precision frequency measurement apparatus. By c; employing a non-oscillating receiver, no sigtion is nals are heard which shows that no energy modulation is present and therefore none of the usual disturbing effects on other receivers due to energy modulation would be present. But with an oscillatin receiver the region of zero beat is broadened by an amount depending on the value of the condenser 17 employed, or if a fixed condenser is used as is indicated in Figs. 1 and 2 of the accompanying drawings, the zero beat band is broadened depending uponthe value of inductance 14 which is effectively connected with condenser 7.

A variationof from to 200 cycles is readily obtained in the 4000 kilocycle band by employing a condenser of 50 micromicrofarads. The rate of this variation may be determined by the frequenc of the energy supplied the windings of t e relay. As a check on the accuracy of the frequency measurements, such a circuit arrangement as herein described may be provided with a frequency doubler actuated from the output of this circuit. The frequency variations in the 8000 kilocycle band then measured will be found to be twice as great as the frequency variations observed in the 4000 kilocycle band. This may also be substantiated without using a frequency doubler, by simply observing with a sensitive receiver the harmonics of the circuit herein described. Had the modulation been energy modulation, the use of the frequency doubler would not have increased the s read of the signals in the upper harmonic ands. Actually, the spread- '1 lng out of the signals by this type of modularoportional to the order of the harmonic, eing three times as much in the 12,000 kilocycle band as in the 4000 kilocycle band and four times as much in the 16,000 kilocycle band as in the 4000 kilocycle band. The frequency characteristics of the output circuit may be varied in many different ways either b varying the capacity or by varying the in uctance. effected in any part of the output circuit of the thermionic tube oscillatory circuit.

I realize that many modifications of my invention are possible other than those shown in the accompanying drawings and described in the fore oing s ecification and it is to be clearly un erstoo that the embodiments of my invention are not to be restricted by the foregoing specification or by the accompany` in'g drawings but only by such restrictions as are imposed by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A frequency modulation system comprising in combination a thermionic oscillator tube, mput and out ut circuits therefor, a mechanically vibrat' e element connected in the input`c1rcuit, and means in the output circuit for periodically varying the frequency This varlation may be i.:

1,sa1,eas

characteristics of said output circuit and the -frequency of the energy transferred to said output circuit.

2. A frequency modulating system comprising in combination a thermionic tube, input and out ut circuits therefor, a mechanically vibratlle element connected in said inut circuit, said output circuit comprisin inductance and capacity, and means 1n sai output circuit for periodically changingthe yfrequency characteristics of said output ciry cuit.

3. A 'frequency modulating system comrising in combination a thermionic oscilator tube, input and output circuits therefor, a piezo electric crystal connected in the input circuit of said tube, and means in the output circuit for varying the frequency ,characteristics of said output circuit at a rate bination a thermlonic tube an input circuit and an output circuit there or, a mechanically vibratile element included in said input circuit for controlling the frequency characteristics thereof, inductance and capacity elements for controlling the frequencr characteristics of said output circuit, an means in said output circuit for periodically varying the frequency characteristics o f said 'output Y A Y i 7. In a frequency modulation system,`a

f comprising a condenser microphone,

put circuit, whereb'ythe frequency "ofthev' generated energy is varled.

6. In a frequency modulation system, a'

thermionic tube, input and out ut circuits therefor, a piezo electriccrystal e ementconnectcd in said in vut circuit, an outputl coil.

connected in sai output circuit, a control Acircuit connected in parallel-with at least a part of said output coil, said control circuit comprising a condenser and a periodic ins terrupter, whereby thefrequency ofthe outof said tube is varied.

thermionic tube, input thermionic tube, input and out ut circuits therefor, a piezo electric crystal e ement connected in said input circuit, means for tuning said output circuit,and means for periodically Varying saidtuningmeans.

- f ALB RT H. TAYLOR.

ins.

therefor, a piezo electric crystale ement oonnected `in said in connected 1n sal part of said output coil, said control circuit whereut circuit, an output coily output circuit, a controll circuit connected in parallel with `at least a by the-frequency of the. output of said tube' I is varied. 18. a vfrequency modulation system, 

